• 터널과지하공간
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• 제8권2호
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• pp.87-95
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• 1998

Field instrumentation and numerical analysis by the finite difference method were applied to estimate the relaxed zone in a subway tunnel of shallow depth in soft rock, excavated by NATM. The convergence and ground displacement can be used to estimate the deformation behavior and the relaxed zone. Parameters for the several models previously suggested were measured using regression analysis techniques adopting a function of time and the face advance. The estimated relaxed zone by the MPBX and FDM analysis were 1.5~3.0 m and 1.5~2.0 m, respectively. It was concluded that the visco-elastic model and the time-dependent elasto-plastic model correlate very well ($r^2$>0.9) with results of the numerical analyses.

• 한국구조물진단유지관리공학회 논문집
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• 제8권2호
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• pp.195-204
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• 2004

본 연구에서는 약액주입 사질고결토에 대해 일정재하크리프시험과 반복재하크리프시험을 실시하여 점 탄소성 거동 규명과 크리프예측을 수행하였다. 일정재하크리프 시험결과 총 변형률은 탄성, 소성 그리고 점탄성변형률로 구분되었으며 이러한 변형률은 응력의 증가에 비례하여 증가하였고 회복된 변형률은 제하시간에 무관함을 알았다. 일정재하크리프시험 예측결과 일반화된 모델과 지수함수모델은 시험결과와 잘 일치하였다. 반복재하크리프시험에서 순간회복변형률은 반복횟수에 무관하였고 누적소성 변형률은 반복횟수에 따라 증가하였으며 응력레벨에 비례함을 알 수 있었다. 반복재하크리프시험의 예측결과 첫 사이클에서는 잘 일치하였으나 반복횟수가 증가함에 따라 약간의 오차가 발생되었다.

• Geomechanics and Engineering
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• 제36권2호
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• pp.167-181
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• 2024

The soil-structure relative stiffness is a key factor affecting the seismic response of underground structures. It is of great significance to study the soil-structure relative stiffness for the soil-structure interaction and the seismic disaster reduction of subway stations. In this paper, the dynamic shear modulus ratio and damping ratio of an inhomogeneous soft soil site under different buried depths which were obtained by a one-dimensional equivalent linearization site response analysis were used as the input parameters in a 2D finite element model. A visco-elasto-plastic constitutive model based on the Mohr-Coulomb shear failure criterion combined with stiffness degradation was used to describe the plastic behavior of soil. The damage plasticity model was used to simulate the plastic behavior of concrete. The horizontal and vertical relative stiffness ratios of soil and structure were defined to study the influence of relative stiffness on the seismic response of subway stations in inhomogeneous soft soil. It is found that the compression damage to the middle columns of a subway station with a higher relative stiffness ratio is more serious while the tensile damage is slighter under the same earthquake motion. The relative stiffness has a significant influence on ground surface deformation, ground acceleration, and station structure deformation. However, the effect of the relative stiffness on the deformation of the bottom slab of the subway station is small. The research results can provide a reference for seismic fortification of subway stations in the soft soil area.

• Journal of Welding and Joining
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• 제25권1호
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• pp.63-69
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• 2007

Once assessment of material failure characteristics is captured precisely in a unified way, it can bedirectly incorporated into the structural failure assessment under various loading environments, based on the theoretical backgrounds so called Local Approach to Fracture. The aim of this study is to develop a numerical fatigue test method by continuum damage mechanics applicable for the assessment of structural integrity throughout crack initiation and structural failure based on the Local Approach to Fracture. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, is developed and employed in the 3-D FEA code in order to numerically evaluate the material and/or structural responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations for each material, are implemented in numerical fatigue test method. The material constants selected from constitutive equations are used directly in the failure assessment of material and/or structures. The performance of the developed system has been evaluated with assessing the S-N diagram of stainless steel materials.

• 한국농공학회논문집
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• 제49권6호
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• pp.47-54
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• 2007

This paper is on the research of the special character of the dynamic response according to a design of the clamped reinforced concrete slab. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The design factor, which affect the dynamic response of the reinforced concrete slab, are the steel layer thickness, steel layer depth, steel layout method, steel layout angle and the slab thickness and span ratio. The main purpose of this study was to find out the dynamic response of the reinforced concrete slab according to above variables. The reduction of deflection/thickness ratio appeared less than 2% when the slab thickness between 20 and 21cm. It is desirable that the slab thickness must be above 20-21cm. The reduction ratio of deflection is appeared greatly when the value of the span/thickness ratio is between 25 and 30. In conclusion, the steel layer depth and thickness had a little effect on deflection of the dynamic response, but had no effect on the steel layout angle.

• 한국농공학회논문집
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• 제49권4호
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• pp.43-49
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• 2007

The reinforced concrete slab is one of main structure members in the construction industry sector. However, most of researches regarding to RC slabs have been focused on two-dimensional Mindlin-type plate element on the basis of laminated plate theory since three-dimensional solid element has a lot of difficulties in finite element formulation and costs in CPU time. In reality, the RC slabs are subjected to dynamic loads like a heavy traffic vehicle load, and thus should insure the safety from the static load as well as dynamic load. Once we can estimate the dynamic behaviour of RC slabs exactly, it will be very helpful for design of it. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The applicability of the proposed finite element has been tested for dynamic behaviour of RC slabs with respect to characteristics of concrete materials in terms of cracking stress, crushing strain, fracture energy and Poisson's ratio. The effect on dynamic behaviour is dependent on not crushing strain but cracking stress, fracture energy and Poisson's ratio. In addition to this, it is shown the damping phenomenon of RC slabs has been identified from the numerical results by using Rayleigh damping.

• Geomechanics and Engineering
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• 제28권2호
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• pp.171-180
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• 2022

Time-dependent stress-strain behaviour significantly influences the compressibility characteristics of the clayey soil. In this paper, a series of oedometer tests were conducted in two loading patterns and investigated the time-dependent compressibility characteristics of Indian Montmorillonite Clay, also known as black cotton soil (BC) soil, during loading-unloading stages. The experimental data are analyzed using a new non-linear function of the Elasto-Visco-Plastic Model considering Swelling behaviour (EVPS model). From the experimental result, it is found that BC soil exhibits significant time-dependent behaviour during creep compared to the swelling stage. Pore water entrance restriction due to consolidated overburden pressure and decrease in cation hydrations are responsible factors. Apart from it, particle sliding is also evident during creep. The time-dependent parameters like strain limit, creep coefficient and C_αe/C_c are observed to be significant during the loading stage than the swelling stage. The relationship between creep coefficients and applied stresses is found to be nonlinear. The creep coefficient increases significantly up to 630 kPa-760 kPa (during reloading), and beyond it, the creep coefficient decreases continuously. Several parameters like loading duration, the magnitude of applied stress, loading history, and loading path have also influenced secondary compressibility characteristics. The time-dependent compressibility characteristics of BC soil are presented and discussed in detail.

• 한국농공학회논문집
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• 제50권2호
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• pp.19-26
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• 2008

This study has been carried out to investigate the dynamic characteristics of RC slabs. For this purpose, the 20-node solid element has been used to discretize the RC slabs into two parts of concrete and rebar. The material non-linearity considering elasto-visco plastic model and the smeared crack model have been adopted in the finite element formulation. The applied load can handle step load, load intensity of harmonic load, area of distributed load and frequency. The frequency of harmonic load has an significant effect on dynamic behaviour in terms of displacement. As the frequency is increased, the effect of load amplitude is more serious. Especially, if the frequency of harmonic load exceeds 30 Hz, it is noted that the displacement by harmonic load is greater than that by step load. In case of harmonic load, the damping effect shows no certain tendency with respect to frequency of load. In details, the damping is effective when the frequency of harmonic load is 2 Hz, but there is no consistent tendency according to damping ratio. The dynamic response when the frequency of harmonic load is 3 Hz shows same result for undamped case as well as for damped case with 5% damping ratio. It is also noted that we can get the largest deflection for damped case with 1% damping ratio. However, there is not any damping effect when the frequency of harmonic load is greater than 4 Hz.

• 한국지반공학회논문집
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• 제24권5호
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• pp.107-115
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• 2008

본 연구는 1차압밀 중의 크리프의 영향과 Yin이 제안한 탄-점-소성 모델에 대한 적용성을 검토하였다. 탄성모델을 이용한 일반적인 압밀이론은, 1차압밀 과정을 표현할 수 있으나 2차압밀을 표현할 수 없다. 이러한 결과는 2차압축을 표현할 수 있는 점성에 기인하며, 때로는 Ladd 등(1977)이 제안한 가정 A 및 B와 같은 스케일효과(실험실 공시체와 현장조건 사이의 점토층 두께의 차이)와 관련되어진다. 통상적으로 1차압밀 중의 크리프의 존재는 많은 연구자에 의해 확인되어졌으며, 가정 B가 잘 맞는 것으로 되어있다. 한편, 대형압밀시험을 통해 가정 A와 B의 중간적인 특성이 Aboshi(1973)에 의한 가정 C로써 제안되어졌다. 본 연구에서는 1차압밀 중의 침하-시간관계에 대한 크리프의 영향을 명백히 하기 위해, peat와 점토에 대해 분할형 압밀시험기를 이용하여 가정 B의 압밀시험을 행하였다. 그리고 Yin의 탄-점-소성 모델을 이용하여 실험결과를 해석하였다. 얻어진 결과는 다음과 같다. 1차압밀 종료시에 분할 공시체의 압축은 과잉간극수압 소산속도의 차이에 의해 동일하지 않았다. 또한 분할형 압밀시험기에 의해 측정된 평균변형률과 Yin의 EVP 모델을 이용한 해석치는 잘 일치하였다. 그러나 과잉간극수압의 소산에 대해서는 측정치가 Yin 모델에 비해 빨리 소산되었다.